I propose to study the sequential neuronal maturation, the normal architecture and the fibrillar-neuronal organization of the human cerebral cortex and cerebellar cortex in normal as well as abnormal (mentally retarded) fetuses, premature newborns and young infants. These studies will be carried out primarily with the rapid Golgi method and in addition with other more routine neurohistological methods. The human studies will be complemented whenever possible or necessary by developmental studies of the mammalian cerebral cortex in selected experimental animals (the cat and the hamster) and utilized in comparative analysis with those of man.